Lubricating compositions containing phosphonic acid salts



United States Patent,

2,991,244 LUBRICATING COMPOSITIONS CONTAINING PHOSPHONIC 'ACID SALTSWarren C. Pattenden, Courtright, Ontario, and Richard J.

Plumstead and Samuel B. Baker, Sarnia, Ontario, Canada, assignors toEsso Research and Engineering Chmpany, a corporation of Delaware NoDrawing. Filed Dec. 31, 1957, Ser. No. 706,289 3 Claims. (Cl. 252-325)This invention relates to lubricating oil compositions containing saltsof phosphonic acid. Particularly, the invention relates to lubricatingfluids and greases improved in their oxidation resistance, load-carryingand anti-wear properties by certain metal salts of phosphonic acid.

It has been found that metal salts of high molecular weight hydrocarbonphosphonic acids containing 10 to 30 carbon atoms can be used to thickenlubricating oil to form greases having high dropping points. In additionthe phosphonic acid salts can also be used in combination with otherthickening agents, such as metalcarboxylates and metal sulphonates.

The phosphonic acids used in preparing the salts of the invention havethegeneral formula:

wherein R may be any hydrocarbon group containing 1 to 30 carbons. Suchhydrocarbon groups may be saturated or unsaturated, aliphatic, aromatic,or cyclic, e.g., alkyl, aryl, cycloalkyl or alkenyl radicals. Specificexamples of these phosphonic acids will include cetane phosphonic acid,dodecane phosphonic acid, ethane phosphonic acid, benzene phosphonicacid, toluene phosphonic acid, cyclohexane phosphonic acid, cyclopentanephosphonic acid cetene phosphonic acid and octadecene phosphonic acidsThe metal component of the phosphonic acid salt can be any metal used inthe grease-making art, e.g., aluminum. However, it is preferably analkali metal such as sodium, lithium, potassium or an alkaline earthmetal, such as calcium, barium, strontium and magnesium.

The phosphonate salt is formed by neutralizing the phosphonic acid witha metal base such as hydroxide, or oxide of the desired metalconstituent, e.g., Ca(OH) The reaction mixture is then heated todehydrate and to remove the water of reaction.

While the preformed phosphonates may be directly added to oil and greasecompositions, it is more advantageous to form the salt in situ in atleast a portion of the lubricating oil to thereby obtain a finerdispersion of the salt in'oil. Thus, the phosphonic acid,if oilinsoluble,

may be first dissolved in hot water, oil added and then the metal base(generally also in a water solutionladded.

The metal salts of lower molecular weight hydro- 'above described saltcompositions include saturated and r 2,991,244 Ice Patented July 4, 19612 l However, if the phosphonic acid is oil-soluble, then it may, ofcourse, be directly dissolved in the oil and neutralized. Generally, thephosphonic acids having eight or more carbon atoms will be oil-soluble,while those having less than eight carbon atoms will be oil-insoluble.In eithercase, the reaction mixture is next heated to a temperature ofabout 212 to 600 F., in order to complete the reaction and to dehydratethe mixture. After dehydration, the oil-salt product may then be furtherblended with other oil or grease materials to form a finished lubricant.The finished lubricant, particularly if it is a grease, can then behomogenized by passing it through a Travis mill, a Morehouse mill or aGaulin homogenizer C fattyacids; high molecular weight C to C fattyacids, as well as the metal salts of high molecular weight sulphonicacids. One of the main advantages pf these ,mixed-saltsystems is that ahighermolecular Weightsalt .tends tomaintainlower molecular weight saltsstably suspended inoil. Thus, ethane phosphonate by itself,-will tend toeventually settle out of oil. However, if ahigher molecularweight salt(e.g. 'astearate) is. also present, a stable dispersion is obtained.Thus, if one component of the mixed=salt is a low. molecular weight.phos} phonate (i.e. C or .less) then one of the other salts presentpreferably will have at least six' or more carbon atoms. Of course, thelower molecular weight P1105:-

phonate may bevstably suspended in oil by other means, such as otherthickening. agents, e.g. polyethylene and carbon black, as wellas otherdispersing agents. 7 7

Suitable low molecular weight acids for forming the unsaturated,substituted and unsubstituted aliphatic monocarboxylic acids and theiranhydrides' having about 1 to 6 carbon atoms "per molecule." These acidsinclude fatty acids'such a's acetic, propionic, "and'similar acidsinclud- Acetic acid or The intermediate molecular weight fatty acidsoperable for the salt formation include those aliphatic,'saturated orunsaturated, unsubstituted monocarboxylic acids Containing? to 12carbonatoms'per molecule, e.g., capric, caprylic, nonanoic, lauricacids, etc.

The high molecular weight fatty acids or aliphatic monocarboxylic acidsuseful for forming the salt thickeners of the invention includenaturally-occurring or synstearic, behe'nic, montanic, linolinic,'linol'eic, ai'achidic, .ricinoleic, oleic, hydrogenated fish oil,tallowacids, etc.

The sulphonic acids used in forming metal salts as oil thickeners aregenerally the high molecular weight (e.g.

;300 to 650-) alkyl aryl sulphonic acids." 'One source of these acids isby the t-reatment of petroleum-oilsio f the lubricating oil range withfuming sulphuric acidL lrSti ch sulphonic acids and their salts havebeenfdesoribedflin nu Pa ts ster r e. .Ui 1,4 7, 17?! 51:

pure alkyl aryl sulphonic acids having from about to 33 carbon atoms permolecule. For example, sulphonated products of alkylated aromatics, suchas benzene, toluene, xylene, etc., alkylated with olefins or olefinpolymers of the type of polypropylene, polyisobutylene, etc. can beused. Specific examples of such sulphonates include: petroleum sulphonicacid, C alkyl benzene sulphonic acid, C alkyl benzene sulphonic acid andC alkyl benzene sulphonic acid.

The metal component of salts of the above fatty acids and sulphonicacids can be any of those previously described as operable in formingthe phosphonate. Generally, alkali and alkaline earth metals will beused. Again, such carboxylates and sulphonates may be preformed and thendispersed in the oil composition, or they too can be formed in situ inthe oil by neutralizing the acid with a metal base.

The lubricating oil used in the compositions of the invention may be amineral lubricating oil, a synthetic lubricating oil, or mixturesthereof. Synthetic lubricating oils which may be used include esters ofdibasic acids (e.g., di-2-ethy1 hexyl sebacate); esters of glycols(e.g., C Oxo acid diester of tetraethylene glycol); complex esters(e.g., the complex ester formed by reacting one mole of sebacic acidwith two moles of tetraethylene glycol and two moles of Z-ethyl-hexanoicacid); formals, silicones, carbonates, polyglycols and other syntheticlubricating oils known in the art.

Various other additives may also be added to the lubricating compositionin amounts of about 0.1 to 10.0 weight percent, based on the totalweight of the composition. Examples of such additives include: viscosityindex improvers such as polyisobutylene; corrosion inhibitors such assorbitan monooleate; pour depressants; detergents; dyes, and the like.

The lubricant compositions of the invention will therefore compriselubricating oil and about .05 to 30, e.g., 3 to 24, weight percent ofthe metal salt of the phosphonic acid material. The amount used, willdepend largely upon its purpose. Thus, if a grease is desired and thephosphonate is to be used as the sole thickener, then generally about 10to 30 weight percent of the total composition will be phosphonate, while.05 to 10 weight percent of the phosphonate material will generallysuflice to impart antioxidant or load-carrying ability to a lubricant.The phosphonate may be used as the sole salt component of the lubricant,or it may be used in the form of a mixedsalt. Such mixed-salts, in turn,will generally comprise in a molar ratio about .1 to 100, e.g., 0.2 to70 moles of phosphonate per mole of a carboxylate and/or sulphonate. Thefatty acids used in forming the carboxylate may consist entirely of lowmolecular weight fatty acid, intermediate molecular weight fatty acid orentirely of high molecular weight fatty acid or blends of these threetypes of fatty acids in any proportion. Fluid lubricants containing themixed-salts are best prepared by heating the mixed-salt materialdispersed in oil to temperatures of about 300 to about 430 F., while thegreases containing mixed-salts are best prepared by heating to about 430to 700 R, where complexing occurs and optimum thickening power isobtained. However, the fluid lubricants can also be prepared at thesehigher temperatures, i.e.,

430 F. and above, while the greases may also be prepared at the lowertemperatures, i.e., less than 430 F.

The invention will be further understood by the following examples:

EXAMPLE I 300 SUS at 100 F., and a viscosity index of 70 was then addedslowly to the paste with constant stirring. Next, a water slurrycontaining 3.3 grams of lithium hydroxide monohydrate (LiOHH O) and 10.0grams of water was added to the oil-phosphonic acid solution in order toneutralize the acid. Next, the grease was dehydrated by heating it on ahot plate for about 1 hour until a final temperature of 400 F. wasreached. The grease was then cooled to about 150 F., and homogenized bypassing through a Travis mill.

EXAMPLE H A grease was prepared in a manner similar to that in Example Iexcept that the phosphonic acid was dodecane phosphonic acid and themetal base was calcium hydroxide, i.e. Ca(OH) EXAMPLES 111 AND IV-AGreases containing mixed phosphonates were prepared in the generalmanner of Examples I and 11 except that the phosphonic acid was amixture of a low molecular weight phosphonic acid and a high molecularweight phosphonic acid and the grease composition was heated to a finaltemperature of 500 F.

EXAMPLE IV-B The composition of Example IV-A was cut back by simplemixing with additional mineral oil to form a liquid lubricant containing6 weight percent of the mixed phosphonate.

EXAMPLE V A grease was prepared by dispersing 13.0 parts by weight ofethane phosphonic acid in water, heating to about 210 F., then adding76.8 parts by weight of oil and 9 parts by weight of calcium hydroxideas a water slurry. Then, 1.2 parts by weight of a calcium sulphonateconcentrate was added. The concentrate consisted of 30% by weight ofpetroleum sulphonate and wt. percent mineral oil. The sulfonate had anaverage molecular weight of about 700. The composition was heated todehydration and finally finished by heating to 500 F., then cooled.

EXAMPLE VI A grease was prepared in the same manner as Example V exceptthat 5.5 parts by weight of cetane phosphonic acid was added in place ofthe 13 parts by weight of ethane phosphonic acid and calcium acetate inan aqueous dispersion was added instead of the calcium sulphonate.

The compositions of several of the preceding examples were tested forwater absorption as follows: grams of grease is worked with 20 cc. ofwater for 300 strokes in an ASTM grease worker. This procedure isrepeated again and again until free water is observed after the last 300strokes. At this point, the test is stopped and the weight percent,based on the weight of dry grease, of water absorbed into the grease isdetermined. Greases having an ability to absorb large quantities ofwater, without losing their structure are particularly desirable sincethey may be used in applications where the grease is exposed tomoisture.

Several of the preceding grease compositions were also tested for theiroxidation resistance by packing 3.0 grams of the grease into a weighedball-and-roller bearing, suspending the bearing in an oven maintained at250 F. and periodically re-weighing the bearing to determine the weightloss of the grease.

The compositions of Examples I to VI in terms of their originalingredients and some of the physical properties of these compositionsare summarized in the following table:

Table I Example Composition (wt. percent) I II 111 IV-A IV-B V VI Octanephosphonic acid 19. 3 4. 1. 5. 5 Dodecane phosphonic acid... 15. 2 3. 5Ethane phosphonic acid 8. 7 10. 0 2. 75 13. 0 LiOHJ-LO 3. 3 7. 8 Oa(OH)-4. 8 7. 8 2. 9. 0 1. 3 Calcium sulphonate (sol. of 30 Wt. percentsulphonate in oil). 1. 2 alcium mam 1s. 2 Mineral Oil (50 SUS at 210 F.)77. 4 80.0 80 78. 2 94. 0 76. 8 80. 0 Max. Temp. of manufacture, "F 400400 500 500 500 500 500 Prrpefities ASTM worked penetration 60 s ro es:

77 F.mIn./l0 274 335 397 288 fluid 348 314 10,000 strokes pene r i n 306Dropping Point, F 500+ 500+ 500+ 500+ 500+ 408 Water absorption beforesaturated (wt. percent based on wt. of grease) 50.0 105 OxldationResistance (wt. percent 1oss)- 300 hours 9. 0 5. 0 12. 0 ,600 hours.--13.0 -10.0 17.0 900 hours--- 21. 0 13. 0 20. 0 1,200 hours 23.0 15.0Falex load-carrying, lbs- 4, 500

4-ba1l Wear Test (1 hr.1,800 r.p.m.-15

Kg.77 F.) Wear Scar dia., mm 0. 366 0. 428

As seen from the above table, the phosphonates of the tron resistance bypacking 5 grams of the composition invention may be used as the solethickening agent to form greases having high dropping points, goodstability in the presence of water, low wear characteristics and highload-carrying ability as well as fluid lubricants (see Examples I toIV-B). Examples V and VI illustrate the use of other salts as asupplemental thickening aid. The oxidation resistance of the phosphonategreases tested (Examples I, IV-A and VI) was exceptionally good, sinceby comparison a commercial grease thickened with lithium-calcium soap of12-hydr0xy stearic acid showed a weight percent loss of 18% at 300hours; 53 weight percent loss at 600 hours and 57 weight percent loss at900 hours; whereas the product of Example containing only about 7 weightpercent of phosphonate showed only 20.0 weight percent loss after 900hours. By the same token, the wear scar diameters of 0.366 mm. and 0.428mm. for the greases of Examples -IV-A and VI respectively compared wellto a wear scar diameter of 0.426 mm. for the previously mentionedcommercial grease.

To illustrate the use of synthetic oils as the base oil, the followinggrease was prepared.

EXAMPLE VII A grease composition was prepared from 5 grams of cetanephosphonic acid, 15 grams of ethane phosphonic acid, 12 grams of Ca(OH)and 68 grams of a methyl phenyl silicone oil having a viscosity at 100F. of 73 centistokes. The grease was prepared in the general mannor ofExample 1, except that the maximum temperature employed was 300 F. Aftercooling and homogenization, a smooth light colored grease was obtainedhaving an ASTMworked 60 strokes penetration of about 250 mm./10 at 77 F.

EXAMPLE VIII 2.9 wt. percent of the neutral sodium salt of l-dodecanephosphonic acid was mixed with 97.1 wt. percent of a base grease. Thisaddition was carried out by adding a water solution of the phosphonateto the grease (which had been preheated to 300 F.). This mixture wasmaintained at 300 F. until dry, then heated to 420 F. and next allowedto cool to 140 F. while stirring. After reaching 140 F., the mixture wasallowed to cool without stirring. The base grease used above consistedof 1 wt. percent of phenyl-alpha-naphthylamine, 23 wt. percent of sodium12-hydroxy stearate, 1.8 wt. percent of a sodium petroleum sulfonate ofabout 375 molecular weight, and 74.2 Wt. percent of mineral oil of 500SUS viscosity at 100 F. and a V1. of 90. The phosphonate containinggrease composition was next tested for oxidainto a bearing, and hangingthe bearing in an oven maintained at 300 F. After 3,000 hours, thegrease composition had reached a micropenetration of 5, which indicatedthe extent of its useful lubricating life, and had sufiered a weightloss of 42%. The base grease without the phosphonate, had an indicateduseful lubricating life of only 1,100 hours in the same test, and aweight loss of 48% at the end of the 1,100 hours. The use of 3 wt.percent trisodium phosphate with the base grease increased its life toonly 1,500 hours. It is thus seen the strong antioxidant efiect of evenminor amounts of the phosphonates of the invention.

EXAMPLE IX Example VIII was repeated but using 2.0 wt. percent of theneutral sodium salt of ethane phosphonic acid with 98.0 wt. percent ofthe same base grease. This composition had a useful lubricating life of1,500 hours, which was a considerable improvement over the 1,100 hourlife of the base grease.

To further illustrate the invention, a lubricant may be prepared in themanner of Example I but using benzene phosphonic acid in place of thecetane phosphonic acid and Al(OH) in place of the LiOI-LH O.

In summary, this invention relates to oil compositions, either fluids orgreases, containing the neutral metal salts of a C to C hydrocarbonphosphonic acid. The preferred form of the hydrocarbon group of thephosphonate will vary widely according to the intended use of thephosphonate. Thus, the hydrocarbon group is preferably a straight chainalkyl group when the phosphonate is used primarily as a thickeningagent, since this form will give the maximum thickening effect. Althoughwhen the phosphonate is utilized because of its other properties, e.g.as an antioxidant, then the nature of the hydrocarbon group is of lessimportance, and straight or branched, saturated or unsaturated, alkyl,aromatic, alicyclic and other hydrocarbon configurations will give aboutthe same result. However, in this latter case, i.e. when the phosphonateis used primarily because of its antioxidant or E.P. properties, then itis generally preferred to use the lower molecular weight hydrocarbonphosphonates, i.e. containing 10 carbon atoms or less. The reason forthis preference being that for properties other than thickening, theeffective function-al portion of the phosphonate is centered about thephosphorus atom.' Thus, lower molecular weight phosphonates can beincorporated in a greater molar proportion into oil than the highermolecular weight phos- 7 phonates to thereby achieve maximumefiectiveness. The phosphonates of the invention can also be used inlubricant compositions supplemented with other thickening agents. Thus,lubricating compositions can be prepared containing 0.5 to 30.0 wt.percent of total mixedsalt materials, a portion of said mixed-salt beinga phosphonate and the remainder being carboxylates and/or sulfonates aspreviously described, or other additive or thickening agents.

What is claimed is:

1. A lubricating oil composition comprising a major amount of minerallubricating oil and about 0.5 to 30 wt. percent of a neutral metal saltof ethane phosphonic acid, said metal being selected from the groupconsisting of alkali metals and alkaline earth metals.

2. A lubricating oil composition comprising a major amount of minerallubricating oil and a thickening amount of a mixture of neutral metalsalts, one salt being a metal salt of ethane phosphonic acid and anothersalt being a salt of a C to C alkyl phosphonic acid, said 8 metal beingselected from the group consisting of alkali metals and alkaline earthmetals and wherein the amount of salt of the ethane phosphonic acid isabout 0.5 to 30.0 wt. percent of the total composition.

3. A lubricating oil composition comprising a major amount of minerallubricating oil and about 0.5 to Wt. percent of a mixed salt material,said material comprising about 0.2 to molar proportions of a neutralmetal salt of ethane phosphonic acid and about one molar proportion of ametal salt of alkyl aryl sulfonic acid of 300 to 650 molecular weightand wherein said metals are selected from the group consisting of alkalimetals and alkaline earth metals.

References Cited in the file of this patent UNITED STATES PATENTS AmottJune 19, 1945 Butcosk Feb. 17, 1953 Hotten et al. June 3, 1958

1. A LUBRICATING OIL COMPOSITION COMPRISING A MAJOR AMOUNT OF MINERALLUBRICATING OIL AND ABOUT 0.5 TO 30 WT. PERCENT OF A NEUTRAL METAL SALTOF ETHANE PHOSPHONIC ACID, SAID METAL BEING SELECTED FROM THE GROUPCONSISTING OF ALKALI METALS AND ALKALINE EARTH METALS.